Generation and biomimetic chemistry of tungsten-dithiolene complexes containing the hydrotris(3,5-dimethylpyrazol-l-yl)borate ligand

Reactions of bis(thio)-W(VI) complexes, LWS2X (L = hydrotris(3,5-dimethylpyrazol-1-yl)borate, X = monoanion), with alkynes produce dithiolene complexes, LWX(dithiolene). The synthesis and characterization of orange LW(OPh) {S2C2(CO2Me)(2)} (1) and burgundy-red LW(SePh) {S2C2(Ph)(2-quinoxalinyl)} (2) and the X-ray crystal structure of 1.0.5CH(2)Cl(2), are described in detail. Crystals of 1.0.5CH(2)Cl(2) are orthorhombic, space group Pbcn, with a = 29.826(6), b = 13.291(4), c = 16.078(3) Angstrom, V = 6373(5) Angstrom(3), and Z = 8. The six-coordinate, distorted-octahedral complex features a tridentate L ligand, a monodentate phenoxide ligand, and a bidentate dithiolene ligand. The short W-S bonds (2.267(4) and 2.279(4) Angstrom) and the parameters associated with the phenoxide ligand (W-O = 1.850(8) Angstrom, W-O-C = 146(1)degrees), point to a considerable degree of W-ligand multiple bonding in the [W(OPh) (dithiolene)](+) unit. For 2, W-Se and average W-S distances of 2.49(2) Angstrom and 2.30(2) ii, respectively, have been obtained from EXAFS studies. The formation of yellow 3,3'-dithiobis [2-(phenyl)thieno[2,3-b]quinoxaline] (3) upon oxidation of 2 supports the likely generation of urothione upon oxidative degradation of molybdopterin-containing tungsten enzymes from hyperthermophilic organisms. (C) 1999 Elsevier Science Inc. All rights reserved.